The Experts below are selected from a list of 171 Experts worldwide ranked by ideXlab platform

Zenghu Chang - One of the best experts on this subject based on the ideXlab platform.

  • approaching the Atomic Unit of time with isolated attosecond pulses
    Conference on Lasers and Electro-Optics, 2014
    Co-Authors: Zenghu Chang
    Abstract:

    Isolated attosecond pulses are powerful tools for studying electron dynamics in atoms, molecules and condensed matter. The shortest pulses achieved so far are 67 as. Challenges and approaches for further shortening such pulses are introduced.

  • Route to One Atomic Unit of Time: Development of a Broadband Attosecond Streak Camera
    Springer Proceedings in Physics, 2012
    Co-Authors: Kun Zhao, Qi Zhang, Michael Chini, Zenghu Chang
    Abstract:

    A new attosecond streak camera based on a three-meter-long magnetic-bottle time-of-flight electron spectrometer (MBES) is developed. The temporal resolution of the photoelectron detection system is measured to be better than 250 ps, which is sufficient to achieve an energy resolution of 0.5 eV at 150 eV photoelectron energy. In preliminary experiments, a 94-as isolated XUV pulse was generated and characterized. With a new algorithm to retrieve the amplitude and phase of XUV pulses (PROOF—phase retrieval by omega oscillation filtering), the attosecond streak camera will be able to characterize isolated attosecond pulses as short as one Atomic Unit of time (25 as).

  • characterizing isolated Atomic Unit attosecond pulses
    Conference on Lasers and Electro-Optics, 2011
    Co-Authors: Michael Chini, Steve Gilbertson, Sabih D Khan, Zenghu Chang
    Abstract:

    Characterizing shorter attosecond pulses has been limited by an approximation in the FROG-CRAB retrieval. We demonstrate a new technique based on interference in laser-assisted photoionization which can characterize ultrabroadband attosecond pulses.

  • extreme ultraviolet supercontinua supporting pulse durations of less than one Atomic Unit of time
    Optics Letters, 2009
    Co-Authors: Hiroki Mashiko, Michael Chini, Steve Gilbertson, Ximao Feng, Chenxia Yun, He Wang, Sabih D Khan, Shouyuan Chen, Zenghu Chang
    Abstract:

    Double optical gating of high-harmonic generation was used to obtain supercontinuous spectra in the extreme UV (XUV) region including the water window. The spectra supported a 16 as pulse duration that is below one Atomic Unit of time (24 as). The dependence of the gated spectra on the carrier-envelope phase of the laser provided evidence that isolated attosecond pulses were generated. In addition, to ensure the temporal coherence of the XUV light, the pulse shape and phase of isolated 107 as XUV pulses using a portion of the spectrum were characterized by attosecond streaking.

  • xuv supercontinua supporting pulse durations of sub one Atomic Unit of time
    Quantum Electronics and Laser Science Conference, 2009
    Co-Authors: Hiroki Mashiko, Steve Gilbertson, Eric Moon, Zenghu Chang
    Abstract:

    Double optical gated high-order harmonic supercontinuous spectra were generated in the extreme ultraviolet region including the “water window”. The spectra supported 16 as pulse durations that are below one Atomic Unit of time (24 as).

H Schmidtbocking - One of the best experts on this subject based on the ideXlab platform.

  • recoil ion and electron momentum spectroscopy reaction microscopes
    Reports on Progress in Physics, 2003
    Co-Authors: J Ullrich, R Moshammer, Alexander Dorn, R Dorner, Ph L H Schmidt, H Schmidtbocking
    Abstract:

    Recoil-ion and electron momentum spectroscopy is a rapidly developing technique that allows one to measure the vector momenta of several ions and electrons resulting from Atomic or molecular fragmentation. In a unique combination, large solid angles close to 4π and superior momentum resolutions around a few per cent of an Atomic Unit (a.u.) are typically reached in state-of-the art machines, so-called reaction-microscopes. Evolving from recoil-ion and cold target recoil-ion momentum spectroscopy (COLTRIMS), reaction-microscopes—the `bubble chambers of Atomic physics'—mark the decisive step forward to investigate many-particle quantum-dynamics occurring when Atomic and molecular systems or even surfaces and solids are exposed to time-dependent external electromagnetic fields. This paper concentrates on just these latest technical developments and on at least four new classes of fragmentation experiments that have emerged within about the last five years. First, multi-dimensional images in momentum space brought unprecedented information on the dynamics of single-photon induced fragmentation of fixed-in-space molecules and on their structure. Second, a break-through in the investigation of high-intensity short-pulse laser induced fragmentation of atoms and molecules has been achieved by using reaction-microscopes. Third, for electron and ion-impact, the investigation of two-electron reactions has matured to a state such that the first fully differential cross sections (FDCSs) are reported. Fourth, comprehensive sets of FDCSs for single ionization of atoms by ion-impact, the most basic Atomic fragmentation reaction, brought new insight, a couple of surprises and unexpected challenges to theory at keV to GeV collision energies. In addition, a brief summary on the kinematics is provided at the beginning. Finally, the rich future potential of the method is briefly envisaged.

Manes Eran - One of the best experts on this subject based on the ideXlab platform.

  • Does Our World “weigh” Less Right Now? The Gravitational Pull in a Scientific Collaboration Network is Getting Weaker with Time
    'HICSS Conference Office', 2020
    Co-Authors: Kelman Guy, Levy Moshe, Manes Eran
    Abstract:

    We study the geographical patterns of scientific collaboration from a large sample of research papers and letters written by two authors that appeared in the magazine Nature over two sub-periods, before and after the popularization of Internet use. We report three results: First, the distance distribution of co-authors is fat-tailed, in agreement with other studies that find gravitational law in collaboration networks. Second, in the later period the distance distribution dominates the range of commute-distance and beyond (>50km), which renders the city the Atomic Unit for statistical testing. Last, strong geographical clustering remains a major generative factor in this network. Assuming the universality of this law, we estimate the gravitational constant from the pull between scientists in the network. We find that this constant has decreased two-fold over the last three decades while the other coefficients remain stable. This may indicate that the gravitational constant absorbs changes in the environment that render distances easier to cross, namely a “lighter world

  • Does Our World “weigh” Less Right Now? The Gravitational Pull in a Scientific Collaboration Network is Getting Weaker with Time
    AIS Electronic Library (AISeL), 2020
    Co-Authors: Kelman Guy, Levy Moshe, Manes Eran
    Abstract:

    We study the geographical patterns of scientific collaboration from a large sample of research papers and letters written by two authors that appeared in the magazine Nature over two sub-periods, before and after the popularization of Internet use. We report three results: First, the distance distribution of co-authors is fat-tailed, in agreement with other studies that find gravitational law in collaboration networks. Second, in the later period the distance distribution dominates the range of commute-distance and beyond (\u3e50km), which renders the city the Atomic Unit for statistical testing. Last, strong geographical clustering remains a major generative factor in this network. Assuming the universality of this law, we estimate the gravitational constant from the pull between scientists in the network. We find that this constant has decreased two-fold over the last three decades while the other coefficients remain stable. This may indicate that the gravitational constant absorbs changes in the environment that render distances easier to cross, namely a “lighter world

Hiroki Mashiko - One of the best experts on this subject based on the ideXlab platform.

Trygve Helgaker - One of the best experts on this subject based on the ideXlab platform.

  • bonding in the helium dimer in strong magnetic fields the role of spin and angular momentum
    Physical Chemistry Chemical Physics, 2020
    Co-Authors: Jon Austad, Alex Borgoo, Erik I Tellgren, Trygve Helgaker
    Abstract:

    We investigate the helium dimer in strong magnetic fields, focusing on the spectrum of low-lying electronic states and their dissociation curves, at the full configuration-interaction level of theory. To address the loss of cylindrical symmetry and angular momentum as a good quantum number for nontrivial angles between the bond axis and magnetic field, we introduce the almost quantized angular momentum (AQAM) and show that it provides useful information about states in arbitrary orientations. In general, strong magnetic fields dramatically rearrange the spectrum, with the orbital Zeeman effect bringing down states of higher angular momentum below the states with pure σ character as the field strength increases. In addition, the spin Zeeman effect pushes triplet states below the lowest singlet; in particular, a field of one Atomic Unit is strong enough to push a quintet state below the triplets. In general, the angle between the bond axis and the magnetic field also continuously modulates the degree of σ, π, and δ character of bonds and the previously identified perpendicular paramagnetic bonding mechanism is found to be common among excited states. Electronic states with preferred skew field orientations are identified and rationalized in terms of permanent and induced electronic currents.